1. Field of the Invention
The present invention relates to a high frequency switch used in a communication apparatus and the like, such as a portable terminal.
2. Related Art of the Invention
An example of a prior art high frequency switch is described in Japanese Laid-Open Patent Publication No. Hei 6-197039.
FIG. 5 is a schematic diagram of a prior art high frequency switch. In FIG. 5, numerals 63, 64 and 65 are capacitors. Numeral 66 is a first strip line. Numeral 67 is a capacitor. Numerals 68 and 69 are resistors. Numeral 71 is a first diode. Numeral 72 is a second strip line. Numeral 70 is a second diode. Numeral 73 is a capacitor. Numerals 74 and 76 are resistors. Numeral 75 is a first control terminal. And, numeral 77 is a second control terminal.
The operation of a prior art high frequency switch having such a configuration is as follows. First, in the case that TX is connected to ANT, a voltage is provided to the first control terminal 75, whereby the first diode 71 and the second diode 70 become ON, whereby TX and ANT are connected. At that time, because of the ON state of the second diode 70, the impedance from TX through the second strip line 72 to RX becomes infinity, whereby no high frequency signal flows to RX when TX is connected to ANT.
Next, in the case that RX is connected to ANT, a voltage is provided to the second control terminal 77, whereby the first diode 71 and the second diode 70 are provided with an inverse bias. Accordingly, a fault switching, does not occur even when a high power signal is input in the normal direction of the diode.
A prior art high frequency switch is as described above. However, in case that a higher power is provided in the prior art configuration, a higher current in the normal direction of each diode 70, 71 is necessary in order to connect TX to ANT. Further, a higher inverse voltage between the anode and the cathode of each diode 70, 71 is necessary in order to satisfy distortion characteristics when RX is connected to ANT.
Here, in order to increase the inverse voltage between the anode and the cathode of each diode 70, 71, it is possible to add an inverse bias circuit composed of resistors 74, 76 and the like. However, this causes a larger circuit scale of the switch, and hence is not advantageous for the use in a small portable terminal and the like, such as a cellular telephone and a PHS.
Further, in the configuration that a circuit other than a diode element (second diode 70) is directly connected on the RX side as shown in the prior art example of the inverse bias circuit composed of the resistors 74, 76 and the like, the isolation possibly degrades when TX is connected to ANT, because an ideal short circuit is not obtained by the ON state of each diode 70, 71.
The present invention has been devised considering such problems. An object of the present invention is to provide a high frequency switch workable on a single power supply, capable of switching without fault switching, and capable of avoiding the degradation of isolation.
One aspect of the present invention is a high frequency switch, comprising:
a first signal terminal;
a first diode the cathode of which is directly or indirectly connected to said first signal terminal;
bias controlling means an end of which is connected to the anode of said first diode;
a second signal terminal directly or indirectly connected to the anode of said first diode;
impedance converting means an end of which is directly or indirectly connected to said first signal terminal;
a serial circuit having high frequency voltage dividing means of dividing high frequency voltage and a second diode, the serial circuit being connected to the other end of said impedance converting means; and
a third signal terminal directly or indirectly connected to said other end of said impedance converting means; wherein
the switching on/off of said bias controlling means implements the conduction between said first signal terminal and said second signal terminal or the conduction between said first signal terminal and said third signal terminal.
Another aspect of the present invention is the high frequency switch of one aspect, comprising short-circuit implementing means connected to the cathode of said second diode for canceling a parasitic component during transmission.
Still another aspect of the present invention is the high frequency switch of one or another aspect, comprising isolation improving means connected to said first diode in parallel.
Still yet another aspect of the present invention is the high frequency switch of any one of one to still another aspects, said high frequency voltage dividing means comprising at least a diode the anode of which is directly or indirectly connected to the cathode of said second diode in series.
A further aspect of the present invention is the high frequency switch of any one of one to still yet another aspects, said high frequency voltage dividing means comprising a resistor directly or indirectly connected to the cathode of said second diode in series.
A still further aspect of the present invention is the high frequency switch of any one of one to still another aspects, said high frequency voltage dividing means being a parallel circuit composing at least a diode the cathode of which is grounded and a resistor.
A yet further aspect of the present invention is the high frequency switch of another aspect, said short-circuit implementing means comprising at least a capacitor.
A still yet further aspect of the present invention is the high frequency switch of another aspect, said isolation improving means comprising at least an inductor and/or at least a capacitor.
An Additional aspect of the present invention is a communication apparatus comprising a high frequency switch of any one of one to a still yet further aspects.
In such a high frequency switch of the present invention, each anode of a first diode and a second diode is connected to the side of a bias control terminal, whereby workability on a single power supply is achieved. Resonance circuits are connected to the first diode and the second diode in order to eliminate the parasitic component of the diodes, whereby the isolation of the switch is improved. High frequency voltage dividing means connected to the first resonance circuit in parallel divides the voltage supplied on the diode into a lower voltage, whereby the distortion characteristics of the diode is improved. Accordingly, fault switching does not occur even when a high power signal is input in the normal direction during the OFF duration of the diode.